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Research Papers

A Fundamental Study and Modeling of the Micro-Droplet Formation Process in Near-Field Electrohydrodynamic Jet Printing

[+] Author and Article Information
William Carter

Graduate Research Assistant
Department of Mechanical,
Aerospace, and Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: cartew3@rpi.edu

George C. Popell

Graduate Research Assistant
Department of Mechanical,
Aerospace, and Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: popelg@rpi.edu

Johnson Samuel

Assistant Professor
Department of Mechanical,
Aerospace, and Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: samuej2@rpi.edu

Sandipan Mishra

Assistant Professor
Department of Mechanical,
Aerospace, and Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: mishrs2@rpi.edu

1Corresponding author.

Contributed by the Manufacturing Engineering of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received August 29, 2013; final manuscript received February 13, 2014; published online April 8, 2014. Assoc. Editor: John P. Coulter.

J. Micro Nano-Manuf 2(2), 021005 (Apr 08, 2014) (12 pages) Paper No: JMNM-13-1067; doi: 10.1115/1.4027099 History: Received August 29, 2013; Revised February 13, 2014; Accepted March 03, 2014

Near-field electrohydrodynamic jet (E-jet) printing has recently gained significant interest within the manufacturing research community because of its ability to produce micro/submicron-scale droplets using a wide variety of inks and substrates. However, the process currently operates in open-loop and as a result suffers from unpredictable printing quality. The use of physics-based, control-oriented process models is expected to enable closed-loop control of this printing technique. The objective of this research is to perform a fundamental study of the substrate-side droplet shape-evolution in near-field E-jet printing and to develop a physics-based model of the same that links input parameters such as voltage magnitude and ink properties to the height and diameter of the printed droplet. In order to achieve this objective, a synchronized high-speed imaging and substrate-side current-detection system is implemented to enable a correlation between the droplet shape parameters and the measured current signal. The experimental data reveals characteristic process signatures and droplet spreading regimes. The results of these studies served as the basis for a model that uses the measured current signal as its input to predict the final droplet diameter and height. A unique scaling factor based on the measured current signal is used in this model instead of relying on empirical scaling laws found in prior E-jet literature. For each of the three inks tested in this study, the average error in the model predictions is under 10% for both the diameter and the height of the steady-state droplet. While printing under nonconducive ambient conditions of low relative humidity and high temperature, the use of the environmental correction factor in the model is seen to result in a 17% reduction in the model prediction error.

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References

Figures

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Fig. 1

Near-field E-jet setup schematic

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Fig. 2

Micro-jet impingement with corresponding substrate-side current spike

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Fig. 3

Trends seen in the process monitoring signals and printing outcomes

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Fig. 4

Time-evolution of droplet volume, diameter, and height

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Fig. 5

Control paradigms for near-field E-jet printing

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Fig. 6

Flowchart outlining modeling approach

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Fig. 7

Stages of meniscus deformation [16]

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Fig. 8

2D droplet shape parameterization

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Fig. 9

3D droplet shape parameterization

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Fig. 10

Overlaid plots of the experimental measurements and the model predictions using environmental correction factor

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